Linear compressor

ABSTRACT

The present invention provides a linear compressor having an elastic body capable of reducing vibration transferred to a shell due to a motion of a moving part. The linear compressor includes a shell defining a hermetic space, a stationary part installed in the shell and having a mass of M b , a moving part reciprocating linearly inside the stationary part at a frequency of ω to compress a fluid, and having a mass of M a , a first elastic body having both ends supported on the moving part and the shell respectively, and having an spring constant of k a , a second elastic body having both ends supported on the shell and the stationary part respectively, and having an spring constant of k b , and a third elastic body having both ends supported on the stationary part and the moving part respectively, and having an spring constant of k. The frequency ω satisfies ω 2 &gt;(k a /M a ). In the above configuration, the spring constant k c  of the third elastic body is always a positive number, so that the third elastic body can be implemented with a mechanical elastic body more easily designed and controlled than a gas elastic body.

TECHNICAL FIELD

The present invention relates to a linear compressor, and more particularly, to a linear compressor having an elastic body to prevent a shell from being vibrated due to a motion of a moving part.

BACKGROUND ART

In general, a compressor is a mechanical apparatus that receives power from a power generation apparatus such as an electric motor or a turbine and compresses air, refrigerant or various operation gases to raise a pressure. The compressor has been widely used in an electric home appliance such as a refrigerator and an air conditioner, or in the whole industry.

The compressor is roughly classified into a reciprocating compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between a piston and a cylinder, and the piston reciprocates linearly inside the cylinder to compress refrigerant, a rotary compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between an eccentrially-rotating roller and a cylinder, and the roller rotates eccentrically along an inner wall of the cylinder to compress refrigerant, and a scroll compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between an orbiting scroll and a fixed scroll, and the orbiting scroll rotates along the fixed scroll to compress refrigerant.

Recently, a linear compressor has been actively developed among the reciprocating compressors. As a piston is coupled directly to a linearly-reciprocating driving motor, the linear compressor can improve the compression efficiency and simplify the configuration without a mechanical loss caused by the motion conversion.

Normally, in the linear compressor, the piston is reciprocated linearly inside a cylinder by a linear motor in a hermetic shell so as to suck, compress and discharge refrigerant. In the linear motor, a permanent magnet is positioned between an inner stator and an outer stator so that the permanent magnet can be driven to reciprocate linearly due to a mutual electromagnetic force. As the permanent magnet is driven in a state where it is coupled to the piston, the piston is reciprocated linearly inside the cylinder to sick, compress and discharge the refrigerant.

Here, while the piston is intendedly reciprocated linearly by driving of the motor, the other components in the shell except an elastic body do not perform an intended motion. Accordingly, hereinafter, the piston and components coupled to the piston to reciprocate linearly with the piston are referred to as a moving part, and components except the moving part are referred to as a stationary part. The stationary part and the moving part are coupled to the shell inside the shell by means of the elastic body. Hereinafter, a vibration system of the linear compressor will be explained as a simple configuration of the shell, the moving part, the stationary part and the elastic body.

In the linear compressor, the stationary part is displaced due to a motion of the moving part, and a force is transferred to the shell coupled to the stationary part by the elastic body, so that the shell vibrates. The vibration of the shell is disadvantageous because it degrades the stability of the linear compressor and muses noise.

FIG. 1 is a view illustrating one example of a conventional vertical linear compressor. A moving part and a stationary part, the stationary part and a shell, and the moving part and the shell are coupled by means of elastic bodies. When the moving part is driven by a motor, three elastic bodies are displaced at the same time. Here, a first elastic body 20 and a second elastic body 21 satisfy the following relation:

$\begin{matrix} {\frac{M_{b}}{M_{a}} = \frac{k_{a}}{k_{b\;}}} & {{Formula}\mspace{14mu} (1)} \end{matrix}$

Here, M_(a) represents a mass of the moving part including a piston 1, an actuator 4 and a magnet member 5, and M_(b) represents a mass of the stationary part including a cylinder 2, a cylinder block 2 a and a cylinder head 3.

In addition, a third elastic body 22 included in the linear compressor is a member improving the efficiency of the linear compressor by coupling the moving part to the stationary part and resonating the moving part during an operation. However, in a state where the first elastic body 20 and the second elastic body 21 satisfy Formula (1), k_(c) must be a negative number so that the third elastic body 22 can satisfy a resonance condition. It is thus impossible to use a mechanical spring which is the most widely-used and easily-controllable elastic body.

DISCLOSURE OF INVENTION Technical Problem

An object of the present invention is to provide a linear compressor having an elastic body capable of reducing vibration transferred to a shell due to a motion of a moving part.

Another object of the present invention is to provide a linear compressor wherein elastic bodies for redwing vibration are all implemented with mechanical elastic bodies.

A further object of the present invention is to provide a linear compressor wherein a moving part moves in a horizontal direction at a frequency of minimizing vibration transferred to a shell due to the motion of the moving part.

Technical Solution

According to the present invention, there is provided a linear compressor, including: a shell defining a hermetic space; a stationary part installed in the shell and having a mass of M_(b); a moving part reciprocating linearly inside the stationary part at a frequency of ω to compress a fluid, and having a mass of M_(a); a first elastic body having both ends supported on the moving part and the shell respectively, and having an spring constant of k_(a); a second elastic body having both ends supported on the shell and the stationary part respectively, and having an spring constant of k_(b); and a third elastic body having both ends supported on the stationary part and the moving part respectively, and having an spring constant of k_(c), wherein the frequency ω satisfies

$\omega^{2} > \frac{k_{a}}{M_{a}}$

In the above configuration, the spring constant k_(c) of the third elastic body is always a positive number, so that the third elastic body can be implemented with a mechanical elastic body more easily designed and controlled than a gas elastic body.

According to another aspect of the present invention, the first and second elastic bodies satisfy

$\frac{k_{b}}{k_{a}} = \frac{M_{b}}{M_{a}}$

In the above configuration, a force transferred to the shell due to a motion of the moving part can be offset, thereby redwing vibration of the shell.

According to a further aspect of the present invention, the spring constant k_(c) of the third elastic body satisfies

$k_{c} = {\frac{M_{a}}{M_{a + M_{b}}}\left( {{M_{a} \cdot \omega^{2}} - k_{a}} \right)}$

and so as to make the moving part resonate. In the above configuration, the linear compressor can operate in a resonance condition.

According to a still further aspect of the present invention, the frequency ω is a resonance frequency ω_(cr) of the moving part.

According to a still further aspect of the present invention, the third elastic body is a mechanical elastic body.

In addition, according to the present invention, there is provided a linear compressor, including: a shell defining a hermetic space; a stationary part installed in the shell and having a mass of M_(b); a moving part reciprocating linearly inside the stationary part at a frequency of ω to compress a fluid, and having a mass of M_(a); a first elastic body having both ends supported on the moving part and the shell respectively, and having an spring constant of k_(a); a second elastic body having both ends supported on the shell and the stationary part respectively, and having an spring constant of k_(b); and a third elastic body having both ends supported on the stationary part and the moving part respectively, and having an spring constant of k_(c), wherein the spring constant k_(c) of the third elastic body satisfies

$k_{c} = {\frac{M_{a}}{M_{a + M_{b}}}\left( {{M_{a} \cdot \omega^{2}} - k_{a}} \right)}$

According to another aspect of the present invention, the first and second elastic bodies satisfy

$\frac{k_{b}}{k_{a}} = \frac{M_{b}}{M_{a}}$

Advantageous Effects

According to the present invention, in a linear compressor, a third elastic body having both ends supported on a stationary part and a moving part respectively and applying a restoring force so that the moving part can operate in a resonance condition can have a positive number as an spring constant.

In addition, according to the present invention, in a linear compressor, an operating frequency is regulated so that a third elastic body can have a positive number as an spring constant.

Moreover, according to the present invention, in a linear compressor, a transfer force transferred to a shell is offset to reduce noise and vibration.

Further, according to the present invention, in a linear compressor, as an spring constant of an elastic body provided so that a moving part can operate in a resonance condition is a positive number, the elastic body can be implemented with a mechanical spring.

Furthermore, according to the present invention, in a linear compressor, a third elastic body can be implemented with a mechanical spring. As compared with a case where the third elastic body is implemented with a gas spring, it simplifies the design, rigidity regulation and control.

Still furthermore, according to the present invention, a transfer force transferred to a shell is offset, so that a linear compressor can operate stably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating one example of a conventional vertical linear compressor;

FIG. 2 is a view illustrating a linear compressor according to an embodiment of the present invention;

FIG. 3 is a schematic view illustrating a vibration system of the linear compressor according to the embodiment of the present invention; and

FIG. 4 is a graph showing a correlation between elastic moduli of first and second elastic bodies and a transfer force of a shell in the linear compressor according to the embodiment of the present invention.

MODE FOR THE INVENTION

Hereinafter, a linear compressor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a schematic view illustrating a vibration system of a linear compressor according to an embodiment of the present invention.

The vibration system of the linear compressor includes a shell 11, a moving part 12, a stationary part 13, a first elastic body 14, second elastic bodies 15 and 16, and a third elastic body 17. Variables used to interpret the vibration system include a displacement x_(a) of the moving part 12, a displacement x_(b) of the stationary part 13, a mass M_(a) of the moving part 12, a mass M_(b) of the stationary part 13, an spring constant k_(a) of the first elastic body 14, an spring constant 0.5·k_(b) of each second elastic body 15 and 16, an spring constant k_(c) of the third elastic body 17, motor parameters L, R, α and V, a motor output F_(m), a force F_(a) applied to the moving part 12 by the first elastic body 14, a force 0.5·F_(b) applied to the stationary part 13 by each second elastic body 15 and 16, an absolute coordinate system N, and each unit vector {right arrow over (i)} and {right arrow over (j)}. Here, the spring constant k_(c) of the third elastic body 17 is a value computed in consideration of an elasticity of a fluid generated when the fluid is compressed due to a motion of the moving part 12. That is, for convenience's sake, a sum of the spring constant of the third elastic body 17 and the spring constant generated due to the compression of the fluid is expressed as the spring constant k_(c).

The shell 11 has a resonance frequency much higher than an operating frequency. Therefore, the vibration system is interpreted on the assumption that the shell 11 is a rigid body. Moreover, in order to interpret a system of the moving part 12, the stationary part 13 and a current, generalized coordinates x_(a)(t), x_(b)(t) and q(t) are necessary.

First of all, kinetic energy T of the vibration system using the above variables is represented by the following formula:

$T = {{\frac{M_{a}}{2}{\overset{.}{x}}_{a}^{2}} + {M_{b}{\overset{.}{x}}_{b}^{2}} + {\frac{L}{2}{\overset{.}{q}}^{2}}}$

In addition, elastic energy V is represented by the following formula:

$V = {{\frac{k_{a}}{2}x_{a}^{2}} + {\frac{k_{c}}{2}\left( {x_{b} - x_{a}} \right)^{2}} + {\frac{k_{b}}{2}x_{b}^{2}}}$

Moreover, damping energy R is represented by the following formula:

$R = {\frac{R}{2\;}{\overset{.}{q}}^{2}}$

Further, a virtual work δW is represented by the following formula:

δW=α·{dot over (q)}·(δx _(a) −δx _(b))−α({dot over (x)} _(a) −{dot over (x)} _(b))δq

Furthermore, Lagrange equation of the vibration system is represented by the following formula:

${{\frac{}{t}\left( \frac{\partial T}{\partial{\overset{.}{p}}_{i}} \right)} - \frac{\partial T}{\partial p_{i}} + \frac{\partial V}{\partial p_{i}} + \frac{\partial R}{\partial{\overset{.}{p}}_{i}}} = Q_{i}$ $Q_{i} = \frac{\partial W}{\partial x_{i}}$

Each of the energy formulae T, V, R and δW induced above is substituted in Lagrange equation as follows:

M _(a) {umlaut over (x)} _(a)+(k _(a) +k _(c))·x _(a) −k _(c) ·x _(b) =α{dot over (q)}(=F _(m))   Formula (2)

M _(b) {umlaut over (x)} _(b) −k _(c) ·x _(a)+(k _(b) +k _(c))·x _(b) =−α{dot over (q)}(=−F _(m))   Formula (3)

L{umlaut over (q)}+R{dot over (q)}+α({dot over (x)} _(a) −{dot over (x)} _(b))=V   Formula (4)

The above Formulae (2) and (3) are expressed as the following determinant:

$\begin{matrix} {{{\left\lbrack \begin{matrix} M_{a} & 0 \\ 0 & M_{b} \end{matrix} \right\rbrack  \begin{Bmatrix} {\overset{¨}{x}}_{a} \\ {\overset{¨}{x}}_{b} \end{Bmatrix}} + {\left\lbrack \begin{matrix} {k_{a} + k_{c}} & {- k_{c}} \\ {- k_{c}} & {k_{c} + k_{b}} \end{matrix} \right\rbrack  \begin{Bmatrix} x_{a} \\ x_{b} \end{Bmatrix}}} = \left\{ \begin{matrix} F_{m} \\ {- F_{m}} \end{matrix} \right\}} & {{Formula}\mspace{14mu} (5)} \end{matrix}$

The transient source F_(m) satisfies F_(m)=F₀e^(jwt) which is a harmonic function. Therefore, the displacements x_(a) and x_(b) of the moving part 12 and the stationary part 13 are expressed as harmonic functions x_(a)=X_(a0)e^(iwt) and x_(b)=X_(b0)e^(iwt), respectively. The displacements expressed as the harmonic functions can be substituted in Formulae (2) and (3) as follows:

$\begin{matrix} {{\begin{bmatrix} {k_{a} + k_{c} - {M_{a} \cdot \omega^{2}}} & {- k_{c}} \\ {- k_{c}} & {k_{c} + k_{b} - {M_{b} \cdot \omega^{2}}} \end{bmatrix}\begin{Bmatrix} X_{a\; 0} \\ X_{b\; 0} \end{Bmatrix}} = \begin{Bmatrix} F_{0} \\ {- F_{0}} \end{Bmatrix}} & {{Formula}\mspace{14mu} (6)} \end{matrix}$

X_(a0) and X_(b0) can be represented by the following formula:

$\begin{matrix} \begin{matrix} {\begin{Bmatrix} X_{a\; 0} \\ X_{b\; 0} \end{Bmatrix} = {\begin{bmatrix} {k_{a} + k_{c} - {M_{a} \cdot \omega^{2}}} & {- k_{c}} \\ {- k_{c}} & {k_{c} + k_{b} - {M_{b} \cdot \omega^{2}}} \end{bmatrix}^{- 1} \cdot \begin{Bmatrix} F_{0} \\ {- F_{0}} \end{Bmatrix}}} \\ {= {\frac{F_{0}}{D} \cdot \begin{bmatrix} {k_{a} + k_{c} - {M_{a} \cdot \omega^{2}}} & {- k_{c}} \\ {- k_{c}} & {k_{c} + k_{b} - {M_{b} \cdot \omega^{2}}} \end{bmatrix} \cdot \begin{Bmatrix} 1 \\ {- 1} \end{Bmatrix}}} \\ {= {\frac{F_{0}}{D}\begin{Bmatrix} {k_{b} - {M_{b} \cdot \omega^{2}}} \\ {{- k_{b}} + {M_{b} \cdot \omega^{2}}} \end{Bmatrix}}} \end{matrix} & {{Formula}\mspace{14mu} (7)} \end{matrix}$

Here, D=(k_(a)+k_(c)−m_(a)·ω²)·(k_(b)+k_(c)−m_(b)·ω²)−k_(c) ².

The sum F_(s) of the transfer forces operating on the shell 11 is represented by the following formula:

F _(s)=(k _(a) ·X _(a0) +k _(b) ·X _(b0))·e ^(jwt)   Formula (8)

The relation of Formula (7) is substituted in Formula (8) as follows:

$\begin{matrix} \begin{matrix} {F_{s} = {\begin{pmatrix} {{{k_{a} \cdot \frac{F_{0}}{D}}\left( {k_{b} - {M_{b} \cdot \omega^{2}}} \right)} +} \\ {{k_{b} \cdot \frac{F_{0}}{D}}\left( {{- k_{a}} + {M_{a} \cdot \omega^{2}}} \right)} \end{pmatrix} \cdot ^{j\; {wt}}}} \\ \left. {= {\frac{F_{0}}{D}{\left( {{{- k_{a}} \cdot M_{b}} + {k_{b} \cdot M_{a}}} \right) \cdot \omega^{2} \cdot ^{j\; {wt}}}}} \right) \\ {= {\frac{F_{0} \cdot w^{2} \cdot \left( {{{- k_{a}} \cdot M_{b}} + {k_{b} \cdot M_{a}}} \right)}{{\left( {k_{a} + k_{c} - {M_{a}\omega^{2}}} \right)\left( {k_{b} + k_{c} - {M_{b}\omega^{2}}} \right)} - k_{c}^{2}}^{j\; {wt}}}} \end{matrix} & {{Formula}\mspace{14mu} (9)} \end{matrix}$

When the force transferred to the shell 11 is offset so that a net force can be zero, vibration of the shell 11 can be reduced. A numerator must be zero in Formula (9) so that the sum F_(s) of the transfer forces can be zero. As F₀ and ω always have values over zero during the operation of the linear compressor, (−k_(a)·M_(b)+k_(b)·m_(a)) must be zero. Therefore, in order to offset the transfer force of the shell 11 and reduce vibration, the mass M_(a) of the moving part 12, the mass M_(b) of the stationary part 13, the spring constant k_(a) of the first elastic body 14 and the spring constant k_(b) of the second elastic bodies 15 and 16 must satisfy the following condition:

$\begin{matrix} {\frac{k_{b}}{k_{a}} = \frac{M_{b}}{M_{a}}} & {{Formula}\mspace{14mu} (10)} \end{matrix}$

Moreover, in the linear compressor according to one embodiment of the present invention, the third elastic body 17 must have a sufficient spring constant to make the moving part 12 resonate. When the transient source F_(m) is zero in Formulae (2) and (3), the spring constant k_(c) of the third elastic body 17 can be expressed as the following determinant:

${{\begin{bmatrix} M_{a} & 0 \\ 0 & M_{b} \end{bmatrix}\begin{Bmatrix} {\overset{¨}{x}}_{a} \\ {\overset{¨}{x}}_{b} \end{Bmatrix}} + {\begin{bmatrix} {k_{a} + k_{c}} & {- k_{c}} \\ {- k_{c}} & {k_{c} + k_{b}} \end{bmatrix}\begin{Bmatrix} x_{a} \\ x_{b} \end{Bmatrix}}} = \begin{Bmatrix} 0 \\ 0 \end{Bmatrix}$

That is, when Relation

{x}={X}e^(iwt)

is used in the form of

[M]{{umlaut over (x)}}+[K]{x}={0},

the following formula is established:

${\begin{bmatrix} {k_{a} + k_{c} - {M_{a} \cdot \omega^{2}}} & {- k_{c}} \\ {- k_{c}} & {k_{a} + k_{c} - {M_{b} \cdot \omega^{2}}} \end{bmatrix}\left\{ X \right\}} = \left\{ 0 \right\}$

Here, a determinant of Matrix [A] must be zero so that Equation [A]{X}={0} can have a feasible solution.

Accordingly, a determinant of [K] is expressed as

(k _(a) +k _(c) −M _(a)·ω²)·(k _(c) +k _(b) −M _(b)·ω²)−k _(c) ²=0

and k_(c) is represented by the following formula:

$\begin{matrix} \begin{matrix} {k_{c} = {- \frac{\left( {k_{a} - {M_{a} \cdot \omega^{2}}} \right) \cdot \left( {k_{b} - {M_{b} \cdot \omega^{2}}} \right)}{\left( {k_{a} - {M_{a} \cdot \omega^{2}}} \right) + \left( {k_{b} - {M_{b} \cdot \omega^{2}}} \right)}}} \\ {= {\frac{M_{a}}{M_{a} + M_{b}}\left( {{M_{a}\omega^{2}} - k_{a}} \right)}} \end{matrix} & {{Formula}\mspace{14mu} (11)} \end{matrix}$

When k_(c) is a positive number, the third elastic body 17 can be implemented with a general mechanical elastic body such as a helical spring. Therefore, when a condition of k_(c)>0 is substituted,

$\omega^{2} > \frac{k_{a}}{M_{a}}$

must be satisfied. In addition, in consideration of the resonance condition of the moving part 12, the frequency ω must be a resonance frequency ω_(cr) of the moving part 12.

The vibration system of the linear compressor was simulated on the basis of the above conditions. It was assumed in the vibration system of the linear compressor that the mass M_(a) of the moving part 12 was 0.6 kg and the mass M_(b) of the stationary part 13 was 5.0 kg. Here, when the spring constant k_(a) of the first elastic body 14 was 1440 N/m, the sum k_(b) of the elastic moduli of the second elastic bodies 15 and 16 satisfying Formula (10) was 1440*(5.0/0.6), namely, 12000 N/m.

When k_(c) satisfying Formula (11) was computed in the above conditions, k_(c) was a positive number, so that the third elastic body 17 could be implemented with an easily-controllable and realizable mechanical spring. In case of a conventional vertical linear compressor, as an spring mutant of a third elastic body satisfying a resonance condition is a negative number, the third elastic body can not be implemented with a mechanical spring. The present invention overcomes sixth a disadvantage of the prior art.

FIG. 4 is a graph showing a simulation result of k_(a) and k_(b) satisfying Formula (7). In Table 1, k_(a) and k_(b) are computed respectively so that the transfer force F_(s) transferred to the shell 11 can be zero.

TABLE 1 Case ka[N/m] kb[N/m] 1 960 8,000 2 1,2000 10,000 3 1,440 12,000 4 1,560 14,000

Here, an operating condition is M-K resonance condition, and an operating frequency of the moving part 12 is 50 Hz, thereby computing k_(c). k_(c) can be computed in consideration of an elasticity of a fluid generated when the fluid is compressed due to the motion of the moving part 12. Moreover, a peak is restricted by the motor parameter α.

Although the preferred embodiments of the present invention have been described, it is understood that the present invention should not be limited to these preferred embodiments but various changes and modifications can be made by one skilled in the art within the spirit and scope of the present invention as hereinafter claimed. 

1. A linear compressor, comprising: a shell defining a hermetic space; a stationary part installed in the shell and having a mass of M_(b); a moving part reciprocating linearly inside the stationary part at a frequency of ω to compress a fluid, and having a mass of M_(a); a first elastic body having both ends supported by the moving part and the shell respectively, and having an spring constant of k_(a); a second elastic body having both ends supported by the shell and the stationary part respectively, and having an spring constant of k_(b); and a third elastic body having both ends supported by the stationary part and the moving part respectively, and having an spring constant of k_(c), wherein the frequency ω satisfies $\omega^{2} > {\frac{k_{a}}{M_{a}}.}$
 2. The linear compressor of claim 1, wherein the first and second elastic bodies satisfy $\frac{k_{b}}{k_{a}} = {\frac{M_{b}}{M_{a}}.}$
 3. The linear compressor of claim 1, wherein the spring constant k_(c) of the third elastic body satisfies ${k_{c} = {\frac{M_{a}}{M_{a + M_{b}}}\left( {{M_{a} \cdot \omega^{2}} - k_{a}} \right)}},$ so as to make the moving part resonate.
 4. The linear compressor of claim 1, wherein the frequency ω is a resonance frequency ω_(cr) of the moving part.
 5. The linear compressor of claim 1, wherein the third elastic body is a mechanical elastic body.
 6. A linear compressor, comprising: a shell defining a hermetic space; a stationary part installed in the shell and having a mass of M_(b); a moving part reciprocating linearly inside the stationary part at a frequency of ω to compress a fluid, and having a mass of M_(a); a first elastic body having both ends supported on the moving part and the shell respectively, and having an spring constant of k_(a); a second elastic body having both ends supported on the shell and the stationary part respectively, and having an spring constant of k_(b); and a third elastic body having both ends supported on the stationary part and the moving part respectively, and having an spring constant of k_(c), wherein the spring constant k_(c) of the third elastic body satisfies $k_{c} = {\frac{M_{a}}{M_{a + M_{b}}}\left( {{M_{a} \cdot \omega^{2}} - k_{a}} \right)}$
 7. The linear compressor of claim 6, wherein the first and second elastic bodies satisfy $\frac{k_{b}}{k_{a}} = {\frac{M_{b}}{M_{a}}.}$ 